Thermodynamic study on refractory metal silicides

Silicon concentration cells used in EMF measurements were composed of SiO2-saturated lithium silicate molten electrolyte and the electrodes of three phases mixture of the compounds in M-Si-O ternary system. Within the experimental temperature range (from 1280 to 1500 K), the activity of silicon at the three phases equilibria of the systems, i.e. Nb5Si3+NbO+SiO2, NbSi2+Nb5Si3+SiO2, TaSi2+Ta5Si3+SiO2, W5Si3+W+SiO2 and WSi2+W5Si3+SiO2, was obtained as a function of temperature. Applying the results, the standard free energy of formation for NbSi2 Nb5Si3, WSi2 and W5Si3 was determined.